Clinical depression, including both bipolar disorders and major depression disorders, is a major public health problem, affecting an estimated 9.5% of the adult population of the United States each year. While it has been hypothesized that mental illness, including mood disorders such as major depression (“MDD”) and bipolar disorder (“BP”) as well as psychotic disorders such as schizophrenia, may have genetic roots, little progress has been made in identifying gene sequences and gene products that play a role in causing these disorders, as is true for many diseases with a complex genetic origin (see, e.g., Burmeister, Biol. Psychiatry 45:522-532 (1999)).
The current lack of biomarkers and the ineffectiveness and reliability of the diagnosis and rates are important issues for the treatment of mental disorders. For example, around 15% of the population suffers from MDD while approximately 1% suffers from BP disorders. Diagnosing bipolar disorder is difficult when, as sometimes occurs, the patient presents only symptoms of depression to the clinician. At least 10-15% of BP patients are reported to be misdiagnosed as MDD. The consequences of such misdiagnosis include a delay in being introduced to efficacious treatment with mood stabilizers and a delay in seeking or obtaining counseling specific to bipolar disorder. Also treatment with antidepressants alone induces rapid cycling, switching to manic or mixed state, and consequently increases suicide risk. Furthermore, in addition to a lack of efficacy, long onset of action and side effects (sexual, sleep, weight gain, etc.), there are recent concerns relating to the undesirable effects of ADs on metabolic syndromes, such as diabetes and hypercholesteremia.